Thermally-tunable liquid lens as a novel alternative to the classical <i>Z</i>-scan method

Abstract This study presents a temperature-tunable liquid lens utilizing silicon oil (SO) to achieve precise focal length modulation without requiring mechanical displacement of the sample, typically required in conventional z -scan methodologies. The lens was fabricated by injecting SO into a cavity formed between two convex glass substrates, with temperature varied from 20 °C to 130 °C to enable a focal length tuning range from 69.30 mm to 77.78 mm, corresponding to an overall change of 8.48 mm. Key performance metrics include a focal length resolution of 7.2 × 10 −2 mm, temperature sensitivity of 1 °C, and demonstrated long-term stability under repeated thermal cycling. The lens’s functionality was validated within a z-scan setup, where it replaced fixed-focal-length optics to eliminate sample translation along the z -axis. Nonlinear refractive index measurements of silver nanoparticles dispersed in distilled water at a concentration of 13 mM yielded a value of (−1.03 ± 0.08) × 10 −7 cm 2 W −1 using the proposed tunable lens, closely matching (−0.97 ± 0.06) × 10 −7 cm 2 W −1 obtained via the conventional z -scan method. The proposed approach provides a practical modification to the classical Z -scan technique by allowing real-time focal control, which can simplify experimental procedures and potentially improve measurement accuracy.